WASHINGTON — When China’s National People’s Congress convened in Beijing in early March, Premier Wen Jiabao highlighted his nation’s military modernization campaign and breathed threats against Taiwan. It would be hard to find a worse time for Europe to offer China military aid.

The United States and Europe have grown apart and no presidential visit will change that. Europe won’t be supplementing the U.S.-led garrison in Iraq, for instance. But Washington might be able to persuade Europe not to raise its ban on arms sales to China.

The fact that the interests of sovereign nations, even ones so closely tied in the past, sometimes diverge shouldn’t surprise anyone. Nevertheless, the United States and Europe share a number of interests, including preserving their generally free and prosperous societies.

No American or European wants to see the rise of a global hegemonic authoritarian power. Like China.

There’s much good that has happened to the People’s Republic of China over the last three decades. However, further liberalization is by no means guaranteed. And even a more democratic China might be aggressively nationalistic.

That wouldn’t be so important if the country was Burma or Zimbabwe, two other states under a European Union arms embargo. But Beijing is likely to eventually marry the world’s largest population with the largest economy.

Even that needn’t be frightening. After all, there were sometimes significant tensions between a rising United States and declining Britain, but they ultimately forged one of the closest international relationships extant.

With China, however, the differences are more significant — and could conceivably lead to war. Should conflict come, it would be in the interests of both the United States and Europe that America prevail.

The EU-implemented an arms embargo after the Chinese regime’s slaughter of demonstrators in Tiananmen Square. But European firms see potential profits from servicing Beijing’s growing arms wants. Some Europeans also hope to advance their goal of becoming a counterweight to America.

The betting now is that the EU will drop the prohibition at its June meeting in Brussels.

If Europe planned on becoming a military counterweight to China, Washington could say go ahead. But despite European talk of establishing an independent foreign policy, even leading nations like Germany have no intention of spending the money necessary to develop serious military capabilities. The obligation for real war-fighting will remain America’s.

Unfortunately, Beijing is thinking about war. Explains Shi Yinhong, professor of international relations at Beijing’s People’s University: “China really wants to have another source for modernizing its military, especially for the possibility of military confrontation with Taiwan.” And confrontation with Taiwan could lead to confrontation with the United States.

Which means high-tech weapons sold by Europe could be used against America. Some EU officials point to Israeli weapons transfers to Beijing, but that is no less an unfriendly act.

Others promise to limit the sort of weapons they sell. But that won’t be much solace should conflict occur.

French Defense Minister Michele Alliot-Marie has argued that European sales might slow Chinese development of its own capabilities. Actually, even European businessmen worry that China wants to appropriate technology as much as acquire weapons.

It’s hard to believe that any voluntary “code of conduct” would be effective.

The best case has been made by British diplomats, who suggest creating a more limited but transparent export control regime. It’s true that European exports, especially of dual-use technology, to China have been rising. Unfortunately, however, the British seem to be about the only ones who are talking about selling less rather than more.

If Europe ignores America’s concerns, the administration’s options are limited. The United States could deny export licenses for sensitive defense sales to companies and nations that sell to China. Beyond that would be the threat of a full-scale trade war, which would be in no one’s interest.

Secretary Rice has called for a “new chapter” in relations. Washington should acknowledge the legitimacy of EU disagreements with American policy and the wisdom of rethinking outmoded institutions, such as NATO.

Most important, the United States must recognize the commercial sacrifice it is asking of the Europeans, while convincing them to look beyond to a future in which China’s positive role is by no means assured. Washington needs to make the argument to individual governments as well as the European Commission, because the European public seems to be on Washington’s side on this issue.

Engagement is a better strategy than isolation for encouraging the development of a free China. However, engagement need not mean strengthening China’s military.

Beijing will become a significant military power with or without European arms sales. There’s no need to hurry the process along.